This invention relates to a technique for preventing diffusion of copper from a wiring layer formed of the copper into an insulator film in a semiconductor device.
To achieve high integration of semiconductor devices, contrivances, such as miniscule patterning and multilayering of circuits, are under way. Among them is a technique for forming a multiplayer interconnection. To impart a multiplayer interconnection structure, an nth wiring layer and an (n+1)th wiring layer are connected together by a conductor layer, and a thin film, called an interlayer insulator film, is formed in a region other than the conductor layer.
An aluminum (Al) layer has been used as a wiring layer. In recent years, it has been studied to use copper (Cu), which is lower in resistance than Al and withstands electromigration, as a wiring material. The Cu has a much greater diffusion coefficient than that of Al, and tends to diffuse into silicon and an oxide film.
In using Cu for wiring, therefore, a barrier film about 200 angstroms thick, for example, needs to be formed between the insulator film and the Cu wiring layer in order to prevent Cu diffusion into the device. As a material for the barrier film, the use of TiN, TaN or WN has been considered. With the recent increase in the integration of semiconductor devices, the aspect ratio of a via hole or the like has become greater. Thus, the use of WCxNy with better coverage has been proposed (e.g., see Japanese Unexamined Patent Publication No. Hei 10-209073).
This publication discloses a technology for depositing a thin film of WCxNy having an amorphous structure, by reacting a starting material gas containing W, such as WF6, W(N(CH3)2)6, or W(N(C2H5)2)6, a hydrocarbon gas, such as CH4, and a nitrogen supply source, such as a nitrogen plasma.
However, since the WCxNy film obtained by the above method has an amorphous structure, it crystallizes from the amorphous structure in response to temperature, and this structural change of the film poses the problem of deteriorating the barrier properties.
The object of the present invention is to provide a semiconductor device with a copper diffusion preventing film having high barrier properties, and a method of making the semiconductor device.
To attain this objective, the present invention provides a semiconductor device, which includes: an insulator film formed on a substrate; a wiring layer of copper formed on the insulator film; and a copper diffusion preventing film, formed between the insulator film and the wiring film, that prevents copper diffusion from the wiring layer to the insulator film.
The copper diffusion preventing film is preferably a crystalline film, that, when subjected to X-ray diffraction, shows peaks at a first position at 36 degrees or more, but 38 degrees or less, and at a second position at 42 degrees or more, but 44 degrees or less. The higher the crystallinity of the copper diffusion preventing film, the higher the barrier properties. The crystallinity can be expressed as the half-width of the peak. The copper diffusion preventing film preferably has a half-width of 3.2 degrees or less for the peak at the first position at 36xc2x0 to 38xc2x0, and preferably has a half-width of 2.6 degrees or less for the peak at the second position at 42xc2x0 to 44xc2x0.
The copper diffusion preventing film may be formed from a film containing tungsten and carbon.
The present invention also provides a method of making a semiconductor device, which includes the steps of converting a gas containing tungsten, carbon, nitrogen and hydrogen into a plasma, and forming a crystalline copper diffusion preventing film by means of the plasma, the copper diffusion preventing film containing tungsten, carbon and nitrogen, and, when subjected to X-ray diffraction, showing peaks at a first position at 36 degrees or more, but 38 degrees or less, and at a second position at 42 degrees or more, but 44 degrees or less in X-ray diffraction, wherein a process temperature during formation of the copper diffusion preventing film is 250xc2x0 C. or higher, preferably 250xc2x0 C. to 500xc2x0 C.
Furthermore, the present invention provides a method for producing a semiconductor device, which includes the steps of converting a gas containing tungsten, carbon, nitrogen and hydrogen into a plasma, and forming a crystalline copper diffusion preventing film by means of the plasma, the copper diffusion preventing film containing tungsten, carbon and nitrogen, and, when subjected to X-ray diffraction, showing peaks at a first position at 36 degrees or more, but 38 degrees or less, and at a second position at 42 degrees or more, but 44 degrees or less in X-ray diffraction, wherein a process pressure during formation of the copper diffusion preventing film is 10 pa or less, preferably 5 pa or less.
The gas containing tungsten, carbon, nitrogen and hydrogen preferably includes a hydrocarbon gas. In this case, the hydrocarbon gas preferably has a multiple bond. Also preferably, the gas containing tungsten, carbon, nitrogen and hydrogen includes a carbon-fluorine compound gas.
In performing the method of the present invention, it is preferred to generate a plasma by an interaction between a high frequency wave and a magnetic field, and to convert the gas into a plasma with the use of the plasma.